One of the central questions of developmental biology is how cells generated by cleavage become committed to different developmental fates. This process, termed determination, is poorly understood despite nearly a century of research. One possible mechanism of determination is that maternally specified cytoplasmic components (determinants) are asymmetrically partitioned during cleavage and direct specific developmental programs in the cells that receive them. The long term goal of the proposed research is understanding of the cellular and molecular mechanisms of determination. Understanding the basis for the initiation of developmental programs will help to understand how developmental programming can go awry leading to birth defects and cancer. Specifically, the proposed research includes 1) completion of genetic and phenotypic analysis of four genes encoding functions required for proper cytoplasmic partitioning in early embryos of the nematode Caenorhabditis elegans, 2) isolation of the DNA corresponding to these genes, and 3) identification of additional genes involved in cytoplasmic partitioning or determination of the intestine. Analyses will include large scale mutant hunts using a variety of mutagens to isolate multiple mutations in each of the four known genes, mutant hunts to identify additional partitioning genes, examination of mutant phenotypes by light microscopy, time- lapse video tape recording, immunocytochemistry, and cell lineage analysis. DNA corresponding to these genes will be isolated by chromosome "walking" and transposon "tagging". In addition, mutant hunts to identify maternal-effect lethal mutants that result in failure to execute the developmental program leading to the formation of intestine will be performed. Previous studies show that some of these mutations will affect cytoplasmic partitioning. In addition it is possible that others will affect cytoplasmic factors responsible for the determination of intestine. These mutations provide a unique opportunity to investigate asymmetric cytoplasmic partitioning and its role in determination. Phenotypic analysis provides information about the genetic and cellular control of the process and isolation of the DNA corresponding to the genes is an important first step towards a molecular understanding.